JP6539032B2 - Display control apparatus, display control method, and program - Google Patents

Description

  The present invention relates to image processing technology. In particular, the present invention relates to an image processing technique for improving image quality when the dynamic range of a device is narrow.

  2. Description of the Related Art Conventionally, as a technique for correcting contrast when the dynamic range of a display device is narrow, a dynamic gamma correction technique is known which widens many gradation parts on a histogram that is a distribution of luminance. In addition, even if the original dynamic range of the display device is wide, the dynamic range decreases when the viewer looks at the display device in a bright environment, so gamma correction that enhances the contrast based on the illuminance around the display device There is a technology to perform processing to make

  By the way, as a characteristic of an eye having two photoreceptors of a pyramidal cell and a rod cell, it is known that the working ratio of the two photoreceptors changes according to the brightness. This is because pyramidal cells mainly work in bright places and rod cells mainly in dark places. Such change in visual characteristics due to brightness is called Purkinje transition. While pyramidal cells can recognize RGB three colors, rod cells can only recognize monochrome. Also, rod cells have different central frequencies of sensitivity, so looking at the blue one is more sensitive than looking at the red one. Therefore, when the proportion of rod vision increases in the dark, that is, rod cells work mainly, Purkinje transition causes a phenomenon in which color intensity and color temperature appear different.

  Therefore, Patent Document 1 describes that the color temperature and the color density are corrected according to the Purkinje transition that occurs according to the viewing environment. Specifically, Patent Document 1 describes that image processing is performed so as to increase the color temperature while increasing the color temperature when the environmental brightness and the APL value are lower than predetermined levels. Here, APL is an abbreviation for Average Picture Level, and the APL value is a value obtained by averaging the number of gradations of a single image frame.

Unexamined-Japanese-Patent No. 2006-285063

  One image, which is video content, is created on the assumption that the dynamic range of the display device is, for example, about 2000. However, some display devices actually viewed by the viewer have a dynamic range narrower than 2000 in terms of performance. Further, in the display device, the dynamic range is lowered due to the bright viewing environment, or the light emitted from the projector is reflected by the screen, and the light reflected again by the viewer side is delivered again to the screen. There are things that are down. In such a display device and a viewing environment, the expected appearance of content, that is, a dynamic range of about 2000 is not realized.

  In such a situation, a correction process using a gamma curve is performed to reduce the contrast, but at that time, the image quality deterioration due to the collapse of the bright part occurs. Therefore, by making the color depth darker, processing is performed to bring it closer to the expected appearance, but at that time the color graininess of the dark part occurs. Further, in Patent Document 1, the influence of the Purkinje transition is corrected only when the display and the surroundings are dark, so it is not possible to cope with the reduction of the dynamic range which occurs when the surroundings are bright. The same problem as described above also exists when the dynamic range of the printing apparatus is low or when the dynamic range of the image recording apparatus is low.

  The present invention has been made in view of such problems, and has as its object to bring the image quality when the dynamic range of an apparatus for acquiring image data is narrow close to the image quality when the dynamic range is wide.

As one means for achieving the above object, the display control device of the present invention has the following configuration. That is, a display control apparatus for displaying an image on a display screen, the input means for inputting image data, and the image data input by the input means, the target pixel for the target pixel to be processed in the image The dynamic range reduction ratio is estimated based on acquisition means for acquiring gradation information related to the display screen, display dynamic range information corresponding to the display screen, and generated dynamic range information according to the image represented by the image data. The signal of the pixel of interest is acquired from the image data according to the estimation means for determining the dynamic range and the increase ratio of the saturation at the pixel having high brightness indicated by the According to the gradation information, the target pixel is set to be larger than the increase ratio of saturation in the pixel having low brightness indicated by the information. A correction means for performing correction processing to increase the saturation of colors that takes signal represents, and a display control means for displaying on said display screen an image based on the corrected correction image data by the correction means.

  According to the present invention, the image quality when the dynamic range of the device for acquiring image data is narrow can be made close to the image quality when the dynamic range is wide.

FIG. 2 is a block diagram showing the arrangement of a color correction unit of the image processing apparatus according to the first embodiment; FIG. 1 is a diagram showing an entire configuration of a display device incorporating an image processing device according to a first embodiment. Reference drawing showing CIE standard spectral luminous efficiency. Reference diagram showing spectral sensitivity of photoreceptors. The figure explaining the relationship between an average gradation value and a ratio. FIG. 8 is a view showing the arrangement of a color correction unit of the image processing apparatus according to the second embodiment. Explanatory drawing of the look-up table which correct | amends the hue in 2nd Embodiment. FIG. 8 is a block diagram showing the configuration of a color correction unit of the image processing apparatus according to the second embodiment. The figure explaining the synthetic | combination vision of cone vision and rod vision with respect to the brightness in a visual field. The figure showing the equivalent brightness of red with respect to illumination intensity. FIG. 14 is a block diagram showing the arrangement of a color correction unit of the image processing apparatus according to the fourth embodiment.

  First, with reference to FIGS. 3, 4, 9, 10, the relationship between the brightness around the display device and the Purkinje transition and how the viewer views the image will be described.

  FIG. 3 is a reference diagram showing CIE standard spectral luminous efficiency showing human average visual characteristics. The horizontal axis of FIG. 3 represents the wavelength (nm) of light, and the vertical axis represents the spectral luminous efficiency. Two curves in the figure are a scotopic visual sensitivity curve 41 and a photopic visual sensitivity curve 42. This figure is a graph comparing the characteristics of photopic vision and scotopic vision, and in the photopic visibility curve 42, the peak wavelength of the sensitivity is about 570 nm, and in the scotopic vision sensitivity curve 41. The peak wavelength of sensitivity is about 500 nm. As described above, since the proportion of eye-shadowing increases in dark places, it can be seen from FIG. 3 that in dark places, the viewer will feel bright on the short wavelength side, and the object color will look bluish. On the other hand, since the proportion of cone vision increases in bright places, the viewer feels that the long wavelength side is bright, and it can be seen that the color of the object looks reddish.

  FIG. 4 is a reference diagram showing spectral sensitivity of photoreceptors. This figure is a graph comparing the spectral sensitivity of the cone for each color and the spectral sensitivity of the rod. The four curves in the figure are the spectral sensitivity curve 43 of the rod, the spectral sensitivity curve 44 of the blue cone, the spectral sensitivity curve 45 of the green cone, and the spectral sensitivity curve 46 of the red cone. It can be seen from FIG. 4 that the cones have different sensitivities for the three primary colors blue, green and red, while the rods have one color sensitivity. Further, as described above, since the proportion of rod vision increases in the dark area, it can be seen from FIG. 4 that the color component appears to decrease in the dark area. That is, it can be seen that as the color gets darker, the color looks lighter (the saturation is lower). On the other hand, it can be seen that as the light becomes brighter, the color looks darker (higher saturation). Rod cells and pyramidal cells are widely distributed in a mixed manner on the retina. Since the proportion of eyesight increases in the dark part of the image and the proportion of cone vision in the light part, when an image is focused on the retina, the saturation in the dark part is low due to the characteristics shown in FIG. It looks like, and in the bright part the saturation looks high.

  FIG. 9 is a diagram for conceptually explaining the synthetic view of the cone view and the box view with respect to the in-field luminance. The vertical axis in FIG. 9 is the in-field luminance, and indicates that the in-field luminance is higher, ie, brighter, as it goes up. In the figure, a range 91 is a range of in-field luminance of the dynamic range assumed for the image, and a range 92 is a range of in-field luminance of the dynamic range displayed on the screen. The range 93 is the ratio of the luminance range for cone viewing, the range 94 is the ratio of the luminance range for rod vision, the range 95 is the insufficient luminance range on the bright side, and the range 96 is the insufficient on the dark side The brightness range is

  Pyramidal cells work mainly when the brightness in the field of view is high (bright). On the other hand, rod cells work mainly when the brightness in the visual field is low (dim). For this reason, the in-field luminance range of the cone view and the rod view has a tapered ratio such as the range 93 and the range 94, respectively. Moreover, the synthetic sensitivity of these rod vision and cone vision is the shape which the range 93 and the range 94 synthesize | combined. As can be seen from FIG. 4, the synthetic sensitivity of the cone vision and the rod vision (the range in which the range 93 and the range 94 are combined) is strongly influenced by the cone vision in the bright in-field luminance, and in the dark in-field luminance The influence of body vision becomes stronger.

  Here, the range 91 of the dynamic range assumed for the content (image) and the range 92 of the dynamic range actually displayed on the screen are considered. The dynamic range of BT 709, which is a typical standard for TV broadcasting, is only about 850. Since this is too narrow and whiteout occurs, a high gradation region is folded 200 to 400% in the gamma curve with a normal photographing camera (bi-function). Thus, the range 91 of the dynamic range assumed for the content is about 2000 to 3000.

  The range 92 of the dynamic range actually displayed may be about 500 in the performance of the display device, or about 100 in the influence of external light or reflected light of the display. In such a case, the composite ratio of the cone view and the cone view is different between the assumed dynamic range range 91 and the actually displayed dynamic range range 92. When the composite ratio of the cone vision and the rod vision changes, the appearance of the image is different due to the difference in the appearance of the cone vision and the rod vision.

  In this embodiment, the hue and saturation of the image are corrected by the difference in the ratio to provide a technique for making the image look closer when viewed in the originally assumed dynamic range. Specifically, in the image processing apparatus according to the present embodiment, as described in the description of FIGS. 3 to 4, the hue 95 is corrected as the correction for enhancing the ratio of cone vision in the range 95 lacking on the bright side. Perform one or both of correction to make it reddish and correction to increase saturation. In the image processing apparatus according to the present embodiment, for the range 96 lacking on the dark side, one of the correction to make the hue closer to blue and the correction to reduce the saturation as the correction to increase the ratio of the stereoscopic vision. Or do both.

  Here, it will be described with reference to FIG. 10 how the ratio of the synthetic sensitivity of pyramidal vision and that of cylindrical vision changes depending on the illuminance of illumination, that is, the brightness of the surroundings. FIG. 10 is a diagram showing the equivalent brightness of red to the illuminance. The horizontal axis of the figure is the illuminance of the test illumination, and the vertical axis is the lightness of the red light felt by the subject with respect to the white light of the same brightness as the equivalent lightness of red, expressed in% (percent). Two graphs in the figure are a graph 101 showing the equivalent brightness of red to the change in illuminance, and an auxiliary graph 102. The auxiliary graph 102 is a graph having a relationship of Y = 45 + 10 × Log X where X is the horizontal axis and Y is the vertical axis, and the horizontal axis is represented by a straight line because it is a logarithmic axis.

  As described above with reference to FIGS. 3 and 4, cone vision is highly sensitive to red and rod vision is less sensitive to red. Further, when the illuminance is high, the ratio of cone vision is high, and when the illuminance is low, the ratio of rod vision is high. Therefore, the graph 101 is the result of combining the effects of both of FIGS. 3 and 4 and is considered to indicate the ratio of cone vision.

  The image processing apparatus according to the present embodiment obtains correction parameters for filling the difference between the assumed dynamic range and the actually viewed dynamic range based on the graph of FIG. The auxiliary graph 102 is a graph having a characteristic that the equivalent brightness differs by 10% if the illuminance is different by 10 times. When the slope of the graph 101 is determined by comparison with the auxiliary graph 102, there is a change of 10% or more and 20% or less per 10 times in the region of illuminance 1 to 100, and 10 times in the region of illuminance 1 or less or 100 or more. It can be seen that the change is 5% or more and 10% or less. That is, it has been found that it is appropriate to correct the correction ratio due to the change of the dynamic range in the range of 5 to 20%, averaging 10% every time the dynamic range changes by 10 times.

  Hereinafter, the present invention will be described in detail based on its preferred embodiments with reference to the drawings. In addition, the structure shown in the following embodiment is only an example, and this invention is not limited to the illustrated structure.

First Embodiment
The configuration and operation of the image processing apparatus according to the first embodiment will be described below with reference to FIGS. FIG. 2 is a block diagram showing the overall configuration of a display apparatus incorporating the image processing apparatus according to the present embodiment. The gamma system image quality adjustment unit 21 performs gamma system image quality correction on the input image. The dynamic range estimation unit 22 generates (determines) a reduction ratio of the dynamic range. The color correction unit 23 corrects the color of the image according to the reduction ratio of the dynamic range generated (determined) by the dynamic range estimation unit 22. The linear system image quality adjustment unit 24 performs image quality correction of the linear system. The panel driver 25 converts an image signal into a display panel drive signal. The display panel 26 is a panel that displays an image. Note that the input image is generally obtained by decoding a signal received by an external input or a tuner, so the illustration of the image input unit is omitted.

  The input image input to the present display device is usually a gamma-based image with a gamma value of 2.2. The gamma system image quality adjustment unit 21 performs gamma system image processing such as enlargement and reduction in the gamma system on such an input image. The dynamic range estimation unit 22 generates a dynamic range reduction ratio based on the dynamic range assumed for the content, the actual display device dynamic range, and the dynamic range reduction ratio due to the ambient illumination. Hereinafter, the dynamic range assumed for the content is referred to as an assumed dynamic range, and the dynamic range of the display device is referred to as a display dynamic range.

  The actual display dynamic range is estimated based on the initial value of the display dynamic range and the ambient illumination. The initial value of the display dynamic range is obtained by measuring either the white luminance of the display device or the black luminance or the luminance of gradation = 1 at the time of factory shipment or the like. In the case of the image processing apparatus alone without the panel driver 25 and the display panel 26, the user sets the initial value of the display dynamic range to a value such as 500 or 1000, for example. The environmental illumination can be estimated using an illumination sensor or an illuminance meter (not shown). The dynamic range estimation unit 22 estimates the actual display dynamic range based on the initial value of the display dynamic range obtained in this manner and the environment illuminance. When there is no illuminance sensor or the like, the user sets the actual display dynamic range to an appropriate value.

  The dynamic range estimation unit 22 estimates the reduction ratio of the dynamic range based on the ambient illumination using an illumination sensor or an illuminometer (not shown). The illumination sensor senses ambient illumination. The higher the illumination (brighter), the narrower the dynamic range. When there is no illuminance sensor or the like, the user sets the reduction ratio of the dynamic range based on the environmental illuminance to, for example, a value such as 1⁄5 or 1⁄20.

  For the assumed dynamic range, for example, the initial value is set to 2000, assuming that a predetermined good dynamic range is used between 1000 times and 10000 times. Then, the content to be displayed may allow the user to change the assumed dynamic range within a favorable dynamic range.

The dynamic range estimation unit 22 calculates the reduction ratio SK of the dynamic range as follows based on the assumed dynamic range, the actual display dynamic range, and the reduction ratio of the dynamic range according to the environmental illumination obtained as described above.
SK = DD / CD × K
Here, DD is the actual display dynamic range, CD is the assumed dynamic range, and K indicates the reduction ratio of the dynamic range by the ambient illumination.

For example, in the case where the actual display dynamic range DD = 500, the assumed dynamic range CD = 2000, and the reduction ratio K of the dynamic range according to the environment illumination K = 1/3, the reduction ratio SK of the dynamic range to be calculated is
SK = (500/2000) x (1/3) = 1/12
It becomes. The dynamic range estimation unit 22 inputs the reduction ratio SK of the dynamic range thus calculated to the color correction unit 23.

  The color correction unit 23 performs color correction using the image input from the gamma image quality correction unit and the dynamic range correction magnification obtained from the reciprocal of the reduction ratio input from the dynamic range estimation unit 22. Details will be described later with reference to FIG. When the actual display dynamic range is sufficiently wide and higher than the assumed dynamic range, it is not necessary to perform the color correction process, and the process by the color correction unit 23 is omitted, and the image as it is output. Since the output from the color correction unit 23 is a linear system, the linear image quality adjustment unit 24 performs image quality adjustment such as edge enhancement processing of a linear system. As mentioned above, although the display apparatus which contained the image processing apparatus was shown in FIG. 2, it may isolate | separate from a display apparatus and the structure which connects an image processing apparatus in the front | former stage of a display apparatus may be used.

  Next, the correction for the reduction of the dynamic range will be described using the difference in the appearance of the color depth in the cone view and the rod view. An example of the color correction processing by correcting the saturation which is the color density will be described with reference to FIG. FIG. 1 is a block diagram showing the configuration of the color correction unit 23 of the image processing apparatus according to the first embodiment.

  The line buffer 11 temporarily stores the input image. The Gaussian filter 12 calculates and acquires a nearby average value from nearby pixels of the processing target pixel as the reference tone value. The saturation increasing unit 13 increases the saturation of the processing target pixel. The saturation maintenance unit 14 only performs timing adjustment without changing the saturation of the processing target pixel. The saturation reduction unit 15 reduces the saturation of the processing target pixel. The ratio determining unit 16 determines and distributes the use ratio of each processing target pixel based on the neighborhood average value obtained from the Gaussian filter 12 and the correction magnification of the dynamic range. The multiplication unit 17 multiplies the use ratio obtained from the ratio determination unit 16 with the image for which the saturation is increased, and the multiplication unit 18 uses the use ratio obtained from the ratio determination unit 16 with respect to the image for maintaining saturation. The multiplication unit 19 is a multiplication unit that multiplies the use ratio obtained from the ratio determination unit 16 with the image whose saturation is reduced. The adding unit 20 is an adder that adds the outputs from the three multiplying units 17 to 19.

  The input image is input to the line buffer 11. In the present embodiment, in the case where the input image is an RGB-based color space, the processing is performed after conversion to the luminance / chromic-based color space (YPbPr) for the reason of easiness. Since a normal input image is input by raster scan, the line buffer 11 holds images of the number of lines necessary for the Gaussian filter 12. For example, if the Gaussian filter 12 is a 9 × 9 filter, the line buffer 11 holds an image of nine lines. Since the Gaussian filter 12 calculates only with the gradation value Y of the luminance signal, the storage width of the gradation value Y may be nine lines, and the PbPr signal which is the color difference signal can be calculated on the pixel to be processed It is sufficient to hold only five lines, which is the period until

  The Gaussian filter 12 calculates an average tone value in the vicinity of the current processing target pixel. In place of the Gaussian filter as the Gaussian filter 12, another filter such as an average value filter may be used. When an average filter is used, there is a disadvantage that the influence of a pixel far from the target pixel on the processing target pixel becomes strong, but there is an advantage that the circuit size becomes smaller. If the size of the Gaussian filter 12 is 9 × 9, the size may be slightly smaller, such as 7 × 7 or 5 × 5. For small sizes, the result of the correction process is slightly worse. The smallest circuit scale is to set the processing target pixel itself as the average tone value (reference tone value), but in that case, the image quality is only slightly improved.

  By calculating the average tone value in the vicinity of the processing target pixel as described above, it is possible to easily calculate how bright or dark the processing target pixel is. If the circuit scale can be increased, super pixel processing or division and integration method, which is a type of image area separation, can be performed. By performing image area separation, it is possible to determine an image area including a pixel to be processed. Therefore, when the circuit size is increased, more appropriate correction such as not processing the bright area in the local bright area in the dark area is performed by using the average gradation value of the image area of the processing target pixel. It becomes possible.

  The saturation increasing unit 13 can realize an increase in saturation simply by performing conversion processing so that each of the PbPr signals which are color difference signals becomes 1 to 1.3 times. However, since color collapse occurs in this method, in order to avoid it, the saturation increasing unit 13 may perform conversion processing using a look-up table that performs curve interpolation instead of straight lines. The saturation maintaining unit 14 shifts the processing target pixel by the number of clocks delayed by the processing of the saturation increasing unit 13. The chroma reduction unit 15 can be realized simply by performing conversion processing on each of the PbPr signals which are color difference signals so as to be about 1 to 0.7 times. Note that conversion processing may be performed using a look-up table that performs curve interpolation instead of straight lines, as in the saturation increasing unit 13.

  The correction ratio, which is a value within the value of the reciprocal of the reduction ratio of the dynamic range estimated by the dynamic range estimation unit 22, is input to the ratio determination unit 16. For example, if the reduction ratio of the dynamic range is 1/12, the correction magnification within 12 is input. If a value exceeding 12 times is set as the correction magnification, as a result, the image output from the color correction unit 23 becomes overcorrected. The ratio determining unit 16 calculates usage ratios of the saturation increasing unit 13, the saturation maintaining unit 14, and the saturation decreasing unit 15 with respect to the average tone value based on the input correction magnification and the average tone value.

  Referring to FIG. 10, the change of the equivalent brightness of red with respect to the brightness is approximately linear with respect to the logarithm of the brightness. Since the gradation value having an index of gamma value 2.2 is linear on the logarithmic axis, it is better to change the gradation value substantially linearly. Assuming that the saturation change is set to 0 near the center of the average tone value, the change in saturation causes the saturation to increase as the average tone value increases, and causes the saturation to decrease as the average tone value decreases. It can be realized by reducing it.

  An example in which the use ratio of each pixel is continuously changed according to the average tone value (reference tone value) will be described with reference to FIG. FIG. 5 is a diagram for explaining the relationship between the average tone value and the use ratio. FIG. 5A illustrates the use ratio to the saturation increasing unit 13, and FIG. 5B illustrates the use ratio to the saturation reducing unit 15. In FIG. 5, the horizontal axis indicates the average gradation value, and for example, it is indicated by the gradation value of 8 bits (0 to 255). The vertical axis is the usage ratio output by the ratio determination unit 16. Further, FIG. 5A has a setting graph 51 of the saturation increasing unit 13, a gradation point 52 to be used ratio 0, and a use ratio point 53 in the full gradation value. FIG. 5B has a setting graph 54 of the chroma reduction unit 15, a gradation point 55 for the use ratio 0, and a use ratio point 56 for the 0 gradation value.

  The gradation points 52 and 55 used as the usage ratio 0 are a point that saturation is not increased below the gradation point 52, and a point that saturation is not reduced below the gradation point 55. These two point values are points close to the APL values of the image to be displayed, or in the case of a moving image, points close to the average value of the APL values for each image. Note that these two point values may be the same value or different values.

  The use ratio point 53 in the full tone value determines the maximum use ratio of the output of the saturation increasing unit 13. The maximum use ratio = use ratio point 53. For example, assuming that the increase ratio of the saturation increasing unit 13 is 1.3 times and the use ratio point 53 is 1.0, the saturation increasing unit 13 increases the PbPr signal up to 1.3 times. In addition, assuming that the increase ratio of the saturation increasing unit 13 is 1.3 times and the use ratio point 53 is 0.5, assuming that the saturation reduction processing is not performed, the remaining use ratio 0.5 maintains the saturation Since it is used for the output of the section 14, 1.3 × 0.5 + 1.0 × 0.5 = 1.15, and the saturation increasing section 13 increases the PbPr signal by a maximum of 1.15 times. In the present embodiment, the dynamic range correction magnification is desirably within 12 times. Further, as described above with reference to FIG. 10, when the dynamic range changes by 10 times, it is appropriate to correct within a range of 5 to 20%, averaging 10%. From these things, it is an example of a desirable setting that the increase rate of the saturation increasing portion 13 is 1.3 times and the use ratio point is 0.5, and the maximum is 1.15 times (15% increase).

  The maximum usage ratio of the output of the saturation reduction unit 15 is determined by the usage ratio point 56 in FIG. 5B. The processing based on the usage ratio is the same as the processing by the saturation increasing unit 13, and thus the description thereof is omitted.

  Since the usage ratio of the output of the saturation maintenance unit 14 is the usage ratio of the usage ratio for increasing saturation and the usage ratio for decreasing saturation, the total usage ratio of 1.0 and the usage ratio for saturation increase It becomes what subtracted the use ratio for saturation reduction. That is, the usage ratio of the saturation maintaining unit 14 = 1.0− (the usage ratio of the saturation increasing unit 13 + the usage ratio of the saturation decreasing unit 15). In FIGS. 5A and 5B, the setting graph is a linear expression (straight line) to simplify the description, but the invention is not limited to the linear expression. In FIG. 10, since the characteristic of the actual red equivalent brightness changes in a curved manner with respect to the illuminance, it is more desirable to represent the setting graph as a curve.

  Next, the multiplication unit 17 multiplies the output of the saturation increasing unit 13 by the usage ratio for the saturation increasing unit 13. Similarly, the multiplication unit 18 multiplies the output of the saturation maintenance unit 14 by the usage ratio for the saturation maintenance unit 14, and the multiplication unit 19 multiplies the output of the saturation reduction unit 15 and the usage ratio for the saturation reduction unit 15. Multiply. Then, the adding unit 20 mixes the outputs of the multiplying units 17 to 19 and outputs a combined pixel.

  In addition, it is possible to process with the RGB value as it is without converting it into a color difference signal, though it is complicated. In that case, the neighborhood average value may be determined by the sum of RGB values. Also, in that case, the process for increasing the saturation may be performed using a two-dimensional look-up table that is a curve that spreads the difference between the R and B values, and the process for decreasing the saturation is R and B Use a two-dimensional look-up table as a curve that narrows the difference in values.

  Further, in the present embodiment, an example is shown in which both the process of increasing the saturation of the bright average gradation part and the process of decreasing the saturation of the dark average gradation part are performed, but only one of them may be performed. In this case, it has been confirmed that to some extent the dynamic range appears to be expanded. In order to reduce the number of correction circuits, it is sufficient to carry out only one process. It has been confirmed in an actual image that it is more effective to increase the saturation of the bright part of the average tone value if only one of them is used.

  Further, in the present embodiment, an example in which the processing target pixel is divided into the saturation increasing unit 13, the saturation maintaining unit 14, and the saturation decreasing unit 15 and subjected to different processes, and then mixed by the multiplying units 17 to 19. However, the configuration example is not limited to this. For example, it may be one processing block having means for increasing or decreasing the saturation depending on the value of the average tone value.

  As described above, according to the present embodiment, the image is adjusted by performing at least one of increasing the saturation of the bright average gradation part and decreasing the saturation of the dark average gradation part, which are saturation adjustment processing. Can be shown closely when viewed in the originally assumed dynamic range.

Second Embodiment
Next, as a second embodiment, an example in which the decrease in the dynamic range is corrected will be described, focusing on the difference in the wavelength that is the center of the cone view and the rod view. An example of the color correction process by correcting the hue according to the partial lightness of the image will be described with reference to FIG.

  FIG. 6 is a block diagram showing the configuration of the color correction unit 23 of the image processing apparatus according to this embodiment. The blocks other than the red-direction hue shift unit 61, the hue maintaining unit 62, and the blue-direction hue shift unit 63, which will be described later, are the same as in FIG. The red-direction hue shift unit 61 shifts (shifts) the hue of the processing target pixel in the red direction, the hue maintaining unit 62 keeps the hue of the processing target pixel as it is, matches the timing, and the blue-direction hue shift unit 63 performs processing The hue of the target pixel is shifted in the blue direction.

  In the present embodiment, both the case where the input image is the luminance color difference system color space YPbPr and the case where the input image is the RGB system color space will be described. The method of obtaining the neighboring average tone value of the processing target pixel is the same as the method described in the first embodiment. It is also the same as the first embodiment that the processing target pixel itself can be used as the average tone value. Alternatively, image area separation may be performed to use an average tone value for each image area.

  In the present embodiment, the amount of shifting (shifting) in the red direction and the blue direction is in the range of 5 to 20% per change of 10 times the dynamic range, as in the first embodiment. First, in the case of a luminance color difference signal, the red-direction hue shift unit 61 adds a value of about 0.1 to 0.3 to a value obtained by normalizing a Pr signal, which is a color difference signal, from -1.0 to 1.0. And a value of about 0.1 to 0.3 is subtracted from the normalized value of -1.0 to 1.0 of the Pb signal. Thus, it is possible to simply shift the hue of the processing target pixel in the red direction. If the value is 1.0 or more, the value is limited to 1.0, and if the value is -1.0 or less, the value is limited to -1.0.

  In addition, it is preferable to make it a close value as the value of this addition and subtraction (about 0.1 to 0.3 in the above example). This is because the chromaticity of the achromatic part in the image is not far from the chromaticity curve of the black point radiation. On the contrary, when using very different values as the addition and subtraction values, the achromatic part in the image will be covered with green or purple.

  Further, as described above, since color collapse occurs due to limitation of the values at both ends simply by addition and subtraction, curve interpolation is preferable to avoid it. For example, when adding 0.2, using a lookup table, add 0.2 between -1.0 and 0.6, add 0.15 for 0.7, and add 0.8 Then, conversion processing is performed such that 0.1 is added, 0.05 is added at 0.9, and not added at 1.0. In the case of subtraction, the direction can be reversed so that it does not exceed -1.0 in the same way.

  The hue maintaining unit 62 shifts the image by the number of clocks delayed by the processing of the red-direction hue shifting unit 61. The blue-direction hue shift unit 63 adds a value of about 0.1 to 0.3 to a value obtained by normalizing -1.0 to 1.0 of a Pb signal which is a color difference signal, and adds a Pr signal to -1. A value of about 0.1 to 0.3 is subtracted from the normalized value of 0 to 1.0. Thus, it is possible to simply shift the hue of the processing target pixel in the blue direction. Similar to the red-direction hue shift unit 61, conversion processing may be performed using a look-up table that performs curve interpolation instead of straight lines.

  Also in the second embodiment, FIG. 5 referred to in the first embodiment can be used similarly. Similar to FIG. 1, the ratio determining unit 16 receives the correction magnification for the reduction of the dynamic range. Based on the input correction magnification, usage ratios to the red-direction hue shift unit 61, the hue maintaining unit 62, and the blue-direction hue shift unit 63 are calculated. The relationship between the average tone value and the use ratio is expressed as in the first embodiment, as described in the description using FIG. That is, the usage ratio of the image whose hue is shifted to red, the usage ratio of the image whose hue is shifted to blue, and the usage of the image whose hue is maintained based on the tone value and the average tone value to be set The ratio is output.

  The multiplication unit 17 multiplies the output of the red hue shift unit 61 by the usage ratio for the red hue shift unit 61. Similarly, the multiplying unit 18 multiplies the output of the hue maintaining unit 62 by the use ratio to the hue maintaining unit 62, and the multiplying unit 19 outputs the output of the blue direction hue shifting unit 63 and the use ratio to the blue direction hue shifting unit 63. Multiply. Then, the adding unit 20 mixes the outputs of the multiplying units 17 to 19 and outputs a combined pixel.

  Next, a case where processing is performed with the RGB values as they are without converting into color difference signals will be described. In that case, the neighborhood average value may be determined by the sum of RGB values. In order to shift the hue in the red direction, it is possible to use a lookup table as a curve in which the value of R increases and the value of B decreases. In order to shift the hue to the blue direction, it is sufficient to use a lookup table as a curve in which the value of R decreases and the value of B increases. The look-up table will be described with reference to FIG.

  FIG. 7 is an explanatory diagram of a look-up table for correcting the hue in the second embodiment. FIG. 7A shows a table for shifting the hue in the red direction, and FIG. 7B shows a table for shifting the hue in the blue direction. The horizontal axis of the figure indicates the input tone value, and the vertical axis indicates the output tone value. R and B in the figure indicate the gradation conversion curve of R and the gradation conversion curve of B in the RGB color space.

  FIG. 7 shows a line 71 of output tone values equal to the input tone value, a conversion curve 72 of R tone in the case of shifting the hue in the red direction, and a conversion curve of B tone in the case of shifting the hue in the red direction. 73, there is a conversion curve 74 of R gradation in the case of shifting the hue in the blue direction, and a conversion curve 75 of B gradation in the case of shifting the hue in the blue direction. The curves 72 to 75 for shifting each color are set so that the values of 1.1 to 1.3 times or 0.9 to 0.7 times are made at the central tone value as described above, It is a curve along the same tone value so that there is no color collapse in the bright part and the dark part of the value. By making the curve, which is a look-up table, into such a shape, it is possible to change the hue of the input image, which is RGB data, without color collapse.

  Further, in the present embodiment, an example is shown in which the hue of the bright average gradation part is shifted in the red direction and the hue of the dark average gradation part is shifted in the blue direction. You may do it. In this case, it has been confirmed that to some extent the dynamic range appears to be expanded. In order to reduce the number of correction circuits, it is sufficient to carry out only one process. It has been confirmed in an actual image that it is effective to shift the hue of the bright part of the average tone value to the red direction if only one of the processing is performed.

  Further, in the present embodiment, the processing target pixels are divided into the red direction hue shifting unit 61, the hue maintaining unit 62, and the blue direction hue shifting unit 63, and different processes are performed, and then mixed in the multiplication units 17-19. Although an example is shown, the configuration example is not limited to this. For example, it may be one processing block having means for shifting the hue in the red direction or the blue direction depending on the value of the average tone value.

As described above, according to this embodiment, at least one of shifting the hue of the bright average gradation part in the red direction and shifting the hue of the dark average gradation part in the blue direction, which is the hue adjustment processing, is performed. By doing this, it is possible to make the image look closer as viewed from the originally assumed dynamic range.
Third Embodiment

  Up to this point, the first embodiment in which the saturation is adjusted to correct the decrease in the dynamic range and the second embodiment in which the hue is adjusted to correct the decrease in the dynamic range have been described. Even in the first embodiment and the second embodiment alone, the dynamic range can appear to be expanded, but the side effect that the blue color component which is not desired to be changed is changed along with the change of the red color component to be changed. It will also come out.

  In the first embodiment, since the saturation of the bright area is increased, the red color component is increased in the bright area and at the same time the blue color component is increased. In the dark area, the blue color component is reduced simultaneously with the red color component. It goes down to the ingredients. In the second embodiment, the red color component is increased at the same time as the red color component is increased in the light area, and the blue color component is increased at the same time as the red color component is decreased in the dark area. The present embodiment aims to eliminate these side effects.

  As the present embodiment, correction of the reduction of the dynamic range will be described focusing on both the difference in appearance with respect to the color depth of the cone view and the box view and the difference in the wavelength as the center of sensitivity. The color correction unit 23 in the present embodiment will be described with reference to FIG. FIG. 8 is a view showing the arrangement of the color correction unit 23 of the image processing apparatus according to this embodiment. 8 adds the red-direction hue shift unit 61, the hue maintaining unit 62, and the blue-direction hue shift unit 63 of FIG. 6 used in the description of the second embodiment to FIG. 1 used in the description of the first embodiment. It is That is, the color correction unit 23 of the present embodiment performs saturation and hue adjustment. The description of each block is the same as in FIGS.

  The respective correction processes have been described in the first embodiment and the second embodiment, and thus the description thereof is omitted. The use ratio of the pixels subjected to each correction process is corrected in two types of correction processes for the reduction of the dynamic range, so that correction is performed in duplicate. Therefore, it is appropriate to set the usage ratio to be about half that of the first and second embodiments in the setting of the usage ratio described in FIG. Further, as shown in FIG. 8, it is preferable to correct the hue first and then correct the saturation as shown in FIG. It does not matter if it is done in the reverse order, but it becomes easy to cause color collapse.

  Further, in the present embodiment, an example is shown in which both processing is performed to shift the hue of the bright average gradation part in the red direction and shift the hue of the dark average gradation part in the blue direction. In the case of, it is sufficient to perform only one process. In addition, the example of performing both the process of increasing the saturation of the bright average gradation part and decreasing the saturation of the dark average gradation part was shown, but if the correction circuit is to be reduced, only one process is performed. good.

  In the present embodiment, the red-direction hue shift unit 61, the saturation maintaining unit 13, the hue maintaining unit 62 and the saturation maintaining unit 14, the blue-direction hue shifting unit 63 and the saturation reducing unit 15 , 18 and 19 have been described, but one or two processing blocks having means for shifting the hue in the red or blue direction and increasing or decreasing the saturation depending on the value of the average tone value are also possible. Good.

Fourth Embodiment
Next, as the fourth embodiment, an image processing apparatus having processing blocks for shifting the hue in the red direction or the blue direction and increasing or decreasing the saturation according to the value of the average tone value is different from the first embodiment. The explanation will be focused on

  FIG. 11 is a block diagram showing the configuration of the color correction unit 23 included in the image processing apparatus according to this embodiment. The blocks other than the correction coefficient conversion unit 111, the saturation and hue processing unit 112, the timing adjustment unit 113, the multiplier 114 for Pb, the multiplier 115 for Pr, the adder 116 for Pb, and the adder 117 for Pr are shown in FIG. The description is omitted because it is similar to 1.

  The Pb multiplier 114 performs processing to increase or decrease the saturation of Pb of the processing target pixel, and the Pr multiplier 115 performs processing to increase or decrease the saturation of Pr of the processing target pixel. The Pb adder 116 shifts (shifts) to increase or decrease the blue phase of Pb of the processing target pixel, and the Pr adder 117 increases or decreases the blue phase of Pr to be processed. Shift (shift). The timing adjustment unit 113 delays the timing with respect to the Y signal because Pb and Pr are delayed due to the calculation processing of saturation and hue with respect to Y of the processing target pixel.

  The saturation correction coefficient and the hue correction coefficient output from the correction coefficient conversion unit 111 are the same as the graphs and calculations described in the first and second embodiments, and thus the description thereof is omitted. In the present embodiment, color saturation is less likely to occur if the saturation processing is performed first and the hue processing is performed later. The present embodiment has an advantage that it can be implemented with a circuit configuration smaller than that of the third embodiment.

  In the above embodiments, an example in which the present invention is applied is mainly described on the display device side. However, the present invention can also be applied to the photographing device side and the image recording side. When the present invention is applied to the photographing apparatus side, the ratio of the dynamic range of human vision with respect to the object and the dynamic range for photographing the object and recording it as an image is corrected. The dynamic range of vision is more than one million times in consideration of adaptation, but is between 10,000 and 100,000 times without adaptation. When the dynamic range of shooting and recording in the photographing apparatus is 2000 times, the image processing of the present invention is used to process saturation and hue so as to correspond to the fact that the dynamic range is expanded by 5 times, 1 It is possible to record an image that looks like a 10,000 times dynamic range. The image recorded in this way after the processing is subjected to the processing of saturation and hue as if it was expanded four times using the image processing of the present invention even in a display device with a dynamic range of 500 times, for example. Thus, if the present invention is applied to each of the photographing side and the display side, an image having a saturation and a hue that looks like 10,000 times close to the dynamic range of vision will be viewed on a 500 times display device. .

  Also, it is possible to apply the present invention to a printing apparatus as well. In a printing apparatus, the reflectance of black ink and black toner is several percent, and the reflectance of paper is about 90%, so the dynamic range of printed matter is several tens of times. When the present invention is applied to a printing apparatus, the ratio of the expected value of the dynamic range of the input image to the dynamic range of the printed matter is corrected. That is, the printing apparatus corrects the ratio of the dynamic range of human vision with respect to the object and the dynamic range in which the object is photographed and recorded as an image. For example, when the dynamic range of the printed matter is 30 times and the assumed dynamic range of the input image is 2000 times, the printing apparatus performs the image processing of the present invention with the correction ratio being 67. The printed material obtained after the image processing looks like saturation and hue having a dynamic range 2000 times.

  As mentioned above, although the example of composition which realizes the present invention was explained by each embodiment, the composition which realizes the meaning of the present invention is not restricted to the above-mentioned embodiment. For example, it is obvious that image processing similar to that of the above embodiment can be performed using a microprocessor and a memory. In this case, it takes time, so it is possible to process still images and moving images with low resolution if the processing speed of the microprocessor is sufficiently high.

Other Embodiments
The present invention supplies a program that implements one or more functions of the above-described embodiments to a system or apparatus via a network or storage medium, and one or more processors in a computer of the system or apparatus read and execute the program. Can also be realized. It can also be implemented by a circuit (eg, an ASIC) that implements one or more functions.

11: line buffer, 12: Gaussian filter, 13: saturation increasing unit, 14: saturation maintaining unit, 15: saturation decreasing unit, 16: ratio conversion unit, 17: multiplication unit, 18: multiplication unit, 19: multiplication Part 20: Addition part 61: Red-direction hue shift part 62: Hue-maintenance part 63: Blue-direction hue shift part

Claims (8)

A display control device for displaying an image on a display screen;
Input means for inputting image data;
An acquiring unit for acquiring, from the image data input by the input unit, gradation information related to the target pixel for the target pixel to be processed in the image ;
Estimating means for estimating a reduction ratio of a dynamic range based on display dynamic range information corresponding to the display screen and generated dynamic range information corresponding to an image represented by the image data;
The signal of the target pixel is acquired from the image data according to the reduction ratio of the dynamic range, and the increase ratio of the saturation in the pixel having high brightness indicated by the gradation information is indicated by the brightness indicated by the gradation information. A correction unit that executes a correction process to increase the saturation of the color represented by the signal at the pixel of interest according to the gradation information so that the multiplication factor of the saturation at a low pixel is larger than
A display control unit configured to display an image based on the corrected image data corrected by the correction unit on the display screen. The correction amount of the correction process by the correction means when the reduction ratio of the dynamic range is equal to or more than a predetermined value is larger than that when the reduction ratio of the dynamic range is less than the predetermined value. The display control device according to. And illumination intensity acquiring means for acquiring information on brightness around the display screen ,
3. The apparatus according to claim 1 , wherein the estimating unit estimates the reduction ratio of the dynamic range based on the display dynamic range information, the generated dynamic range information, and the information acquired by the illuminance acquiring unit. The display control device according to. Wherein the correction means, as said generated dynamic range information, the display control device according to claim 2, characterized by using a predetermined value. The acquiring unit acquires gradation information related to the target pixel based on pixel data of peripheral pixels present within a predetermined range from the target pixel among the image data input by the input unit. The display control apparatus according to any one of claims 1 to 4 , which is characterized by the following. The correction means is
Saturation increasing means for performing a first saturation process to increase the saturation of the pixel data of the processing target pixel among the image data input by the input means to obtain saturation increased pixel data;
Saturation reducing means for obtaining a saturation reduced pixel data by executing a second saturation process for reducing the saturation of the pixel data of the processing target pixel among the image data input by the input means;
Among the image data input by the input means, the saturation increase pixel data obtained by the saturation increase means based on the pixel values of peripheral pixels present within the predetermined range from the processing target pixel, and A ratio determining unit that determines a mixing ratio of the saturation reduction pixel data obtained by the saturation reduction unit and the pixel data of the processing target pixel;
The first saturation processing is completed by mixing the saturation increasing pixel data, the saturation decreasing pixel data, and the pixel data of the processing target pixel based on the mixing ratio determined by the ratio determining means. The display control device according to claim 1, further comprising: generation means for generating pixel data. A display control method for displaying an image on a display screen;
An input step of inputting image data;
Acquiring, from the input image data , gradation information related to the target pixel for the target pixel to be processed in the image ;
Estimating the reduction ratio of the dynamic range based on display dynamic range information corresponding to the display screen and generated dynamic range information according to an image represented by the image data;
The signal of the target pixel is acquired from the image data according to the reduction ratio of the dynamic range, and the increase ratio of the saturation in the pixel having high brightness indicated by the gradation information is indicated by the brightness indicated by the gradation information. Performing a correction process of increasing the saturation of the color represented by the signal at the pixel of interest according to the gradation information, such that the magnification is larger than the increase rate of the saturation at the low pixel ;
A display control step of displaying on the display screen an image based on the corrected image data that has been corrected in the correction step. A program for operating a computer as each means of the display control device according to any one of claims 1 to 6 .

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